Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WA6MHZ, Jan 4, 2012.

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  1. K1DNR

    K1DNR Ham Member QRZ Page

    Yes Cecil. Absolutely correct. I spent the day today trimming a dipole that is just a tad larger than 1 wave length on 20m, and pruning it in combination with my home brew ladder line for minimum VSWR(50) at the balun where a short length of coax enters the shack. I'm all about tuning my dipoles with my home brew lines, fed through a balun and coax and the dipoles are rarely 1/2 wavelength, often 1 w/l or somewhere inbetween but it depends on the length of the high Zo line I use to feed it.

    My illustration was to make a point about resonance. This seems to be a misconception - that an antenna has to be resonant.

    We may tune it to resonance with matching, or with a tuning stub, etc - but there is nothing special about an antenna that is, unto itself "resonant".

    I will continue to tune a Hamstick for minimum VSWR(50) at the feed point, assuming the best mounting and rigging procedures are followed. I will not tune it for X=0. Better yet, If I get serious about mobile HF I'll build something better than a Hamstick.

    If I could actually achieve an SWR of 1:1 in a mobile setup, X=0 would be part of the definition. In reality, I will probably not achieve that - so minimum VSWR is the goal - not some other tuning that is GREATER than minimum VSWR just so my analyzer tells me X=0. Or - I could add that shunt coil and really tune the thing. Of course that all goes out the window if we start moving. No pun intended.

    At some point, if we make it to a VSWR(50) of 1:1, the point is moot because X can't be anything else.

    Is that much agreeable?
    Last edited: Jan 25, 2012
  2. W5DXP

    W5DXP Ham Member QRZ Page

    True, but we do indeed invariably make the antenna system resonant. An antenna tuner tunes the antenna system to resonance by achieving a 50 ohm Z0-match at the tuner input, i.e. an SWR of 1:1 just as you say. This can be illustrated by disconnecting the transmitter and shorting out the tuner input terminals. Then use a grid dip meter on the passive antenna system to find that the antenna system is indeed resonant at the desired frequency but (usually) only because of the properly adjusted tuner in the circuit. It's a small point but an important one for newcomers to realize.
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